The invention concerns link belts, and has particular, though not exclusive, reference to link belts as used as conveyor or support structures in the papermaking and related industries.
Conventional link belts comprise a combination of coils produced from monofilament yarns of circular cross-section joined in interdigitated disposition by hinge wires engaged with the overlapping turns of adjacent coils. In a link belt typical of one type of structure the coils are of oval cross-section and have a major inside dimension of 3.75 mm, the monofilament yarn and the hinge wire being 0.55 mm and 0.9 mm in diameter respectively. In such a structure, ready insertion of the hinge wires, particularly by mechanical means, requires that adjacent coils, at least in practical terms be fully engaged one with another, any diviation from such full engagement reducing the transverse dimension of the hinge wire receiving tunnel formed by the overlapping turns of adjacent coils and material deviation reducing such transverse dimension to an extent sufficient to prevent or to make difficult the insertion of the hinge wire.
It is known in the art that tension introduced into close wound coils by opening up the turns thereof to receive an adjacent coil into interdigitated relationship therewith and which arises from the elastic properties of the material of the coil assists in maintaining engagement of one coil with another, such tension causing successive turns of one coil to grip the interposed turns of the next adjacent coil and, if of sufficient magnitude, to prevent separation of such coils.
The tension in the coil is a function of the elastic properties of the material of the coil, and is accordingly determined by, inter alia, the cross-sectional dimension of the polyester monofilament which forms the coil, and reduction in such dimensions giving rise to a corresponding reduction in the gripping effect of the turns of one coil on those of another.
Having regard to possible non-uniformity of the physical characteristics of adjacent coils, to the incidence of secondary twist therein or to other factors, full engagement of adjacent coils may not occur or may not be maintained, with the result that difficulty may be experienced in effecting hinge wire insertion.
A reduction in the diameter of the monofilament from which the coils are formed, the major inside diameter of the coil remaining unchanged, allows of an increase in the cross-sectional dimensions of the tunnel formed by over-lapping turns of adjacent spiral coils by increasing the extent of permitted engagement of one coil with an existing array of connected coils, and would thus facilitate hinge wire insertion. However, such reduction in diameter would also reduce the spring tension in the coil, and thus the gripping effect of one coil on the interposed turns of the next adjacent coil, and would accordingly increase the likelihood of coil separation, thus making worse the very problem sought to be avoided by the reduction. Furthermore, too ready a opening up of the turns of the coil might well give rise to separation in excess of that required and result in a plurality of turns of the adjacent coil being engaged between two successive turns of a given coil.
An object of the present invention is to provide a tunnel of increased cross-sectional dimensions without prejudice to the capacity of the coils to remain in interdigitated disposition, thus to avoid the difficulties experienced in the mechanical insertion of hinge wires into the interdigitated turns of adjacent helical coils to connect the same together.